Orbital developer stream development

ABSTRACT

ELECTROSTATIC LATENT IMAGES ARE DEVELOPED BY DEVELOPER MATERIAL IN A CHAMBER HAVING A CURVED BOTTOM SURFACE BY TRANSMITTING TO THE DEVELOPER MATERIAL IN CONTACT WITH THE CHAMBER SUFFICIENT OSCILLATORY ENERGY TO CIRCULATE A STREAM OF THE DEVELOPER MATERIAL IN AN ORBITAL PATH IN A SUBSTANTIALLY VERICAL PLANE, THE OSCILLATORY ENERGY HAVING AN AXIS OF OSCILLATION PERPENDICULAR TO THE VERTICAL PLANE AND CONTAINING THE UPPER PERIPHERY OF THE STREAM OF DEVELOPER MATERIAL WITH A SURFACE BEARING AN ELECTROSTATIC LATENT IMAGE.

April 13,, 1911 R J. HAGENBACH 3,574,660

ORBITAL DEVELOPER STREAM DEVELOPMENT 2 Sheets-Sheet 1 Filed July 25.1966 INVENTOR. 3 ROBERT J. HAGENBACH ATTORNEY April 13, 1971 HAGENBACH3,574,660v v ORBITAL DEVELOPER STREAM DEVELOPMENT Filed July 25. 1966 2Sheets-Sheet 2 INVENTOR. ROBERT J. HAGENBACH A TTOR/VEY United StatesPatent 3,574,660 ORBITAL DEVELOPER STREAM DEVELOPMENT Robert J.Hagenhach, Rochester, N.Y., assignor to Xerox Corporation, Rochester,N.Y. Filed July 25, 1966, Ser. No. 567,475 Int. Cl. (303g 13/08, 15/08U.S. Cl. 117-175 12 Claims ABSTRACT OF THE DECLOSURE This inventionrelates in general to xerography, and more specifically, to a system fordeveloping electrostatic images.

In the art of xerography, as originally disclosed by Carlson in U.S.Pat. 2,297,691 and as further described in many related patents in thefield, a xerographic plate containing a photoconductive insulating layeris first given a uniform electrostatic charge in order to sensitize itsentire surface. The plate is then exposed to an image of activatingelectromagnetic radiation such as light, X-ray or the like whichselectively dissipates the charge in the illuminated areas of thephotoconductive insulating layer while leaving behind a latentelectrostatic image in the non-illuminated areas. This latentelectrostatic image is then developed by depositing finely dividedelectroscopic marking particles, often referred to in the art as toner,on the surface of the photoconductive insulating layer. Wherenon-reusable photoconductive insulating material is employed, theelectroscopic marking material is fixed in place on the surface of theinsulating material by any convenient means such as by heat fusing.Where a reusable photoconductive insulating material is used, thevisible image formed by the toner particles is transferred to a secondsurface, such as a sheet of paper, and fixed thereon to form a permanentvisible reproduction of the original image.

The most widely employed method of electrostatographic, developmenttoday is cascade development. In cascade development, relatively largecarrier particles are employed to transport finely divided pigmentedelectroscopic marking powder or toner to a latent electrostatic image.The carrier particles are triboelectrically charged with a polarityopposite that of the electroscopic powder. The electroscopic powderelectrostatically adheres to the larger particles of carrier materialand when cascaded over an electrostatic latent image-bearing plate,drum, belt or the like, the powder deposits in the image areas of theplate by a charge which is controlled so as to have a greater attractionfor the electroscopic powder particles than the carrier mateial. Thedeposited particles form a powder image which may be permanently fixedin place or transferred to another suitable support such as a papersheet. Illustrative patents describing the widely used cascade method ofdevelopment include U.S. Pat. 2,573,881 to Walkup et al.; U.S. Pat.2,965,868 to Eichler; U.S. Pat. 2,937,660 to Walkup; and U.S. Pat.2,990,278 to Carlson. In all of the conventional cascade systemsdisclosed by the foregoing patents, it is essential that a developerbucket arrangement for carrier and toner mixing and recycling beincluded in the development system. The presence of 3,5745% PatentedApr. 13, 1971 a bucket conveyo contributes greatly to the size and costof an electrostatographic imaging system. Further, passage of the bucketconveyor system through the developer supply during the mixing andrecycling operations promotes the formation of grit and rapidly reducesdeveloper life. An additional problem encountered in the conventionalcascade process is the occurrence of developer starvation occurs in thedownstream region of the development zone after much of theelectroscopic marking particles carried by the carrier particles havebeen removed by the latent electrostatic image. The depleted or starveddeveloper contributes to the formation of low density images. It is alsowell known that during the cascade process, a powder cloud is generatedas the carrier beads and unused toner particles drop by gravity to thebottom of the development chamber. This powder cloud often causes theformation of an undesirably high background deposit in non-image areas.In addition, drum and carrier abrasion is promoted by the constantimpact of carrier and toner particles cascading across the surface ofthe drum or plate. A further requirement in existing cascade developmentsystems is the need for thorough and uniform mixing of toner and carrierparticles during the recycling and replenishing cycles.

Although the cascade process has proved to be a most effective processfor producing excellent high quality reproductions of line patterns,faithful reproductions of original images comprising solid areas,half-tones, continuous tones or the like, cannot be produced with theconventional cascade development system. It has been found that cascadeprocess reproductions of large black or dark areas are not developeduniformly throughout their entire area but are developed more heavilyaround the edges than in the central portions of the area. Apparently,in order for the electroscopic marking powder to deposit on theelectrostatic latent image and adhere thereto, it is necessary that itbe brought within the influence of electrostatic lines of forceemanating from the image pattern. These lines of force extend betweenpoints of different potential and commonly extend between points on theimage-bearing surface that have a potential gradient between them. Whenthe area of an image pattern has very low contrast from one point to anearby point, the potential gradients are small and the lines of forceset up are consequently less effective during development. This isparticularly true in large solid image areas where there are no nearbypotential gradients on the image surface. The net effect is thatfrequently no development takes place in the center portion of suchareas of uniform potential. It has been found that positioning adevelopment electrode in close proximity to the image-bearing surfaceduring development improves the continuity of the development in lowcontrast image areas. The use of such electrodes in electrostatographicdevelopment processes is well known and disclosed, for example, in U.S.Pats. 2,573,881 and 2,777,418. The improved continuity of developmentapparently is due to the presence of the elec trode which supplies anearby potential gradient for set ting up the electrostatic lines offorce. However, systems in which development electrodes are employedsuffer serious deficiencies in certain areas. Because the developmentelectrode must be spaced as closely as possible to the image-bearingsurface for most effective use, the developing material employed incascade processes tends to bunchup or jam between the image-bearingsurface and the development electrode with consequent smudging of theimage as well as scratching and abrasive deterioration of the imagebearing surface. Further, the flow of developing material over theimage-bearing surface is often impeded by the presence of developmentelectrodes thereby limiting the speed of the development process. Thus,there is a containing need for a better system for developing latentelectrostatic images.

It is, therefore, an object of this invention to provide an improvedsystem for developing electrostatographic images which overcomes theabove-noted disadvantages.

It is another object of this invention to provide a system ofelectrostatographic development which reduces the effects of abrasionpresently encountered in cascade development.

It is a further object of this invention to provide anelectrostatographic developing system which produces images having lessbackground than images produced by conventional cascade developmenttechniques.

It is yet a further object of this invention to provide a developingsystem which is simpler and more compact than conventional developingsystems.

It is another object of this invention to provide an improveddevelopment system which prevents developer starvation.

It is another object of this invention to provide a high speed solidarea development system.

It is still another object of this invention to provide a developercirculating system which promotes more rapid and uniform mixing of tonerand carrier particles.

The foregoing objects and others are accomplished, generally speaking,by providing an electrostatographic de velopment system wherein a latentimage-bearing surface is brought into contact with a stream ofindividually vibrating developer particles moving in a generallycyclical or orbital path. Movement of both the individual developerparticles and the stream is effected by a device which imparts regularoscillatory motion to an arcuate developer chamber within which thedeveloper particles are contained. In this invention, as hereinafterillustrated by a xerographic drum, a drum carrying a latent electostaticimage is at least patrially immersed in a flowing stream of developermaterial comprising conventional electroscopic marking particles with orwithout carrier material.

Electroscopic marking particle and carrier compositions are well knownto those skilled in the art. Representative patents in which thesedeveloper compositions are disclosed include U.S. Pat. 2,618,551 toWalkup, U.S. Pat. 2,618,552 to Wise, U.S. Pat. 2,633,415 to Walkup andWise, U.S. Pat. 2,659,670 to Copley, U.S. Pat. 2,788,288 to Rheinfrankand Jones, and U.S. Reissue Pat. 25,136 to Carlson. Generally, thetoners have an average particle diameter between about 1 and about 30microns whereas the relatively larger carrier beads have an averageparticle diameter from about 50 to about 700 microns in diameter.However, if toner particles are employed without a carrier, larger tonerparticles are preferred for optimum flow characteristics.

According to the present invention, developer material is brought intocontact with an image-bearing surface in a manner such that the numberof contacts between the developer particles and the image-bearingsurface is increased over former techniques. The increase in the numberof contacts is achieved by the employment of a stream of individuallyvibrating developer particles moving in a cyclical path. Most, if notall, of the developer particles in the mass individually possess avibratory movement not necessarily parallel to the stream path. Thevibratory movement of the particles effects both fluidized suspension ofthe individual developer particles and cyclical movement of the totalmass of developer particles. The individual developer particles appearto vibrate in tiny orbits rather than in a linear path and may be theprincipal reason for the improved mixing and cyclical developer streammovement achieved in this system. Due to both the constant vibratorymotion of the individual developer particles and the generally cyclicalmovement of the developer mass, a greater number of different carrierbeads and toner particles are brought into contact with each incrementalarea of the latent imagebearing surface during a given unit of time. Thecirculating developer bath is contained within a rapidly oscillatingchamber having a bottom surface curved generally concentrically aboutthe electrostatographic drum axis. Although the axial cross section ofthe chamber comprises a roughly arcuate configuration, it should beunderstood that the outer shell of the developer chamber may be of anysuitable shape which allows the conditions necessary for development asset forth in the specification to occur. Typical shapes in clude bowl orU shaped developer chambers or variaions thereof. The developer chambermay be modified by making the upstream end of the chamber Wider than thedownstream end or vice versa. Further, bafiies may be employed in thedeveloper housing to promote uniform flow of the developer stream. Theparticular modifiiation, of course, would depend upon the direstion ofthe circulating developer stream and the direction ofelectrostatographic drum rotation. The flow direction of the circulatingdeveloper stream depends upon the direction of oscillatory energyimparted to the developer chamber. The oscillatory energy imparted tothe developer chamber has an axis of oscillation parallel to the axis ofdeveloper stream motion. The direction of developer stream flow may bereversed by reversing the direction of oscillation. Oscillatory motionmay be imparted to the chamber by any suitable means capable ofproducing high frequency oscillatory energy. Typical well known sourcesof high frequency oscillatory energy include electric motors havingfixed or adjustable eccentric Weights attached to the motor armatureshtft and ball type vibrators such as the Vibrolator vibrators sold bythe Martin Engineering Company. The total mass of developer material inthe developer housing, the developer stream velocity desired, the shapeof the developer housing, the frictional characteristics of theparticular developer material being employed, and the total mass ofequipment actually being vibrated all affect the degree of oscillatoryamplitude and frequency necessary to achieve the desired developerstream movement. Typical oscillatory frequencies include a range fromabout 1,000 to about 4,000 regular oscillatory vibrations per minute.Typical vibration amplitudes include from about .0001 to about .25 inch.It is apparent, however, that the energy loss during transmission of thevibratory energy from the energy source to the developer housing shouldbe considered when determining the particular amplitude to be employed.In general, the stream velocity increases with an increase in frequencyThe quality of the developed images appears to be relatively unaffectedby differences between the drum surface speed and the developer streamspeed. Although it is not entirely clear, the formation of high densityimages without an attendant smearing may be due to a combination of anabsence of developer starvation and the gentle fluidlike characteristicsof the developer mass.

Any suitable developer material such as those described above may beemployed. Typical toner concentrations in two component developersystems include from about 0.5 to about 2 percent by weight. The tonerparticles may be replenished by the addition of new toner material ateither end of tfhe developer chamber. Addition of the fresh tonermaterial at the downstream end of the circulating developer material ispreferred when a carrier material is employed because the carriermaterial and the fresh toner material are more thoroughly mixed prior tocontact with the latent image-bearing surface. The supplementary tonermaterial may also be added to the developer stream at any pointintermediate the ends of the developer chamber; maximum mixing occurringwhen the new toner material is added at the downstream end of thechamber.

Any suitable photoconductive surface may be employed in the system ofthis invention. Well known photoconductive materials include vitreousselenium, organic or inorganic photoconductors embedded in anon-photoconductive matrix, organic or inorganic photoconductorsembedded in a photoeonductive matrix or the like. Representative patentsin which photoconductive materials are disclosed include U.S. Patent2,803,542 to Ullrich, U.S.

Patent 2,970,906 to Bixby, US. Patent 3,121,006 to Middleton, U.S.Patent 3,121,007 to Middleton, and U. S. Patent 3,151,982 to Corrsin.

It is obvious that any suitable electrostatographic surface may beemployed for carrying out the method of the instant invention, as forexample, a drum, fiat plate, flexible belt and the like. The surfacesmay either be movable through the development zone or fixed with respectthereto.

The advantages of this improved electrostatographic development systemwill become even further apparent upon consideration of the followingdisclosure of the invention; particularly when taken in conjunction withthe accompanying drawings wherein:

FIG. 1 is a schematic sectional view of one form of apparatus forcarrying out the novel method set forth in the specification.

FIG. 2 is an enlarged schematic view of a modified form of the developerchamber of FIG. 1.

FIG. 3 is a schematic plan view of a modified arrangement of apparatusfor effecting cyclical movement of the developer particles.

FIG. 4 is a schematic sectional view of an alternative form of theapparatus shown in FIG. 1.

Referring now to FIG. 1, reference character designates a rotatablexerographic drum having an outer layer of photoconductive insulatingmaterial such as vitreous selenium. The drum 10 is mounted to move inthe direction indicated by the arrow. The surface of drum 10 isuniformly charged by a conventional corona charging device 12 andexposed to a pattern of activating electromagnetic radiation at 14. Thelatent electrostatic image formed by the exposure means 14 is developedby rotating drum 10 through a stream of circulating developer material16 comprising substantially spherical carrier beads and suitableelectrostatic marking particles contained within chamber 18. As thelatent image-bearing drum surface moves through the moving stream ofvibrating developer particles 16, the latent image is subjected tocontact with developer particles constantly moving into and out ofcontact with the latent image as well as across the image surface in acompound movement. This movement dissipates the effects of undertoned ordetoned carrier particles by causing toned carriers to contact theimagebearing surface at different points along its path of movementthrough the development zone. This constantly occurring exposure to newcarrier particles greatly reduces the possibility of forming low densityimages. Fur brush 20 may optionally be employed to dislodge unwantedcarrier beads at the fringes of developed image areas without adverselyaffecting the developed image. Brush 2% may, if desired, be eliminatedwhen carrier beads having a diameter greater than about 500 microns anda density of 5 or more are employed. The developed image may betransferred at a transfer station 22 to a moving paper web 23. Atransferred powdered image may be permanently fixed to the paper 23 byany conventional means such as heat fusing. The drum It) may then becleaned of any excess toner particles at a cleaning station 24 thuscompleting the entire charging, exposing, developing, transferring, andcleaning cycle.

Both the generally cyclical movement of the total mass of the developerparticles and the vibratory movement of individual developer particlesin the mass are effected by any suitable source of oscillatory energysuch as the schematically illustrated means 26 fastened to the developerhousing 18. For example, a regular oscillatory movement may be impartedto the developer particles by attaching to developer housing 18 a motorhaving unequal eccentric weights 27 mounted on the motor drive shaft 28.Fresh toner may be added at inlet 29 as the circulating developermaterial becomes depleted of toner particles. The vibratory motion ofindividual developer particles circulating in developer housing 18promotes rapid and uniform mixing of carrier particles and newly addedtoner particles. The geometry of the developer housing 18 and thedirection of orbital vibration imparted to the housing 18 may be alteredto control the direction of movement of the developer stream. High speeddeveloper machines require rapidly moving streams of developer material.In order to avoid toner starvation, stagnant areas adjacent theimage-bearing surface are preferably avoided. When a uniform and rapidlymoving stream is desired, curved lips 30 and 32 should be employed toimpart a bottle configuration to the housing 18. The curved lips 30 and32 eliminate the formation of stagnant areas which often occur in thedeveloper material on one or both sides of the developer housing 18. Thecurved lips 30 and 32 function as guides which promote gradual ratherthan abrupt changes in direction of the developer material 16 therebyeliminating eddy currents.

FIG. 2 is an enlarged view of a modified form of the developer housingshown in FIG. 1. The modified housing 50 has a generally U-shapedconfiguration wherein the sides of the U do not contain a curved lip.The small arrows in the developer bath 51 indicate the direction of flowof the developer material. Due to the configuration of housing 50, zonesof different developer velocities occur. These zones are indicated bythe letters A, B and C. The velocity of the mass of developer particlesin Zone B is very high as a result of the influence of gravity and theenergy provided by oscillatory vibrator 52. The rapidly moving developerstream in Zone B promotes the formation of dense toner images byproviding a constant supply of fresh toner to the undevelopedimage-bearing surface of drum 54. The developer patricles in Zone A moveat a relatively low velocity thereby arresting powder cloud formation.Maximum utilization of apparatus employing the type of developer housingshown in FIG. 2 is achieved by rotating the xerographic drum 54 in adirection substantially opposite and parallel to the direction of thedeveloper stream flow. However, the direction of movement of the drumand developer stream may, if desired, be nonparallel. The retardation ofpowder cloud formation in Zone A contributes to the establishment of anideal environment for the developed image-bearing surface as it emergesfrom the developing zone.

Although a particular drum rotation direction and developer circulationdirection are depicted by arrows in FIGS. 1 and 2, good quality imagesare obtained by re versing the direction of the drum and/or thedeveloper stream. The direction of the developer stream may be reversedby merely reversing the orbital direction of the oscillatory energyapplied to the developer housing. Where the orbital energy is applieddirectly to the developer housing by means of a rigidly attachedelectric motor having an offset weight or weights secured to the motorarmature shaft, the direction of the developer stream may be reversedmerely by reversing the direction of rotation of the electric motorshaft. The speed of the developer stream relative to the surface of themoving drum may be less than, equal to or greater than the speed of adrum surface. The speed of the drum may be regulated by any conventionalspeed regulator. The speed of the developer stream may be regulated byadjusting the frequency of oscillatory energy applied to the developerhousing. Generally, the circulating velocity of the developer streamincreases with an increase in oscillatory energy frequency. Similarly,the velocity of the developer particles circumferentially positioned inthe developer housing increases with an increase in developer mass. Thepartcular drum and developer speed to be employed depends upon the drumdiameter, the direction of drum rotation, the direction of developerstream circulation and the length of the development Zone (i.e., thedistance a point on the surface of a drum travels while in contact withthe developer stream).

In FIG. 3, another embodiment of the invention is shown wherein anoscillatory energy source is driven by means remote from the developerhousing. In this embodiment, eccentric weight is mounted on a shaft 102which in turn is journaled in support bearings 104 and 106. Shaft 102 isconnected to pulley 108 by a flexible spring or cable 110 and shaft 112.Shaft 112 is supported by bearings 114 and 116, Rotation of pulley 108is effected by belt 118 driven by pulley 120. Pulley 120 is connected toa reversible motor 122 through a variable speed drive mechanism 124. Theoscillatory energy created by rotation of eccentric weight 100 istransmitted through shaft 102 to bearings 104 and 106. Since bearings10d and 106 are rigidly secured to frame 12-6, the frame 126 oscillatesat the same frequency as the bearings 10-3 and 106. Developer housing128 is secured to frame 126 by means of shafts 130 and 132. Theoscillatory energy transmitted from the eccentric weight 100 throughbearings 104 and 106 to the frame 126 is further transmitted todeveloper housing 128 through supporting shafts 130 and 132. Adevelopment electrode 134 may optionally be attached to the developerhousing 128. The development electrode 134 is supported by insulators136. The development electrode may be electrically connected to asuitable reference potential or to ground as is well known in the art.To facilitate oscillation with minimum restraint, frame 126 is suspendedfrom a support member (not shown) by means of rubber mounts 138, 140,142 and 144. Spring or cable 110 also functions as a means to minimizeloss of oscillatory energy.

In FIG. 4, another embodiment of the invention is shown wherein aflexible xerographic belt supported by three drums is used to permitfull frame exposure. In this embodiment, flexible belt supported byrotating drums 152, 154 and 156 is charged to a uniform potential by acorona charging device 158. The belt 150 is then exposed to activatingelectromagnetic radiation at 160. Development of the thus formed latentelectrostatic latent image is effected by bringing the latentimage-bearing surface into contact with a moving stream of developerparticles 162 contained within arcuate chamber 164. Oscilatory energy istransmitted from a suitable source (not shown) through frame 166 andsupporting shaft 168 to the developer housing 162. The frame 166 isinsulated from a rigidly fixed supporting member 170 by means of helicalsprings 172. The toner image on the belt 150 is transferred to atransfer web 174 and the image subsequently made permanent by heatfusing. The belt 150 is then cleaned at brush 176 after the developingand image transfer cycle are completed.

A development electrode, schematically shown at 178, may be positionedin the developer stream 162 adjacent and parallel to the belt 150. Thedevelopment electrode comprises a series of development electrode wireswhich span the width of the belt 150. These electrode wires 180 may besecured to insulators as shown in FIG. 3. The electrode wires 180 may beeither electrically connected to a suitable reference potential (notshown) or to ground for the establishment of an electric field adjacentthe surface of belt 150. Since the development electrode 178 is securedto oscillating developer housing 164, the electrode 178 also oscilltaesand imparts oscillatory energy to the developer material 162.Alternatively, the electrode may be secured to a suitable stationary support (not shown). A stationary development electrode is preferred at lowdrum speeds and low oscillatory vibra tion frequencies because theformation of striated toner images corresponding to the shape of thedevelopment electrode are avoided. Although the development electrode isdepicted in FIG. 4 as wires 180 extending transverse to the direction ofthe movement of belt 150, the wires may optionally be rotated to anyposition up to 90 (not shown). Further, any other suitable developmentelectrode configuration such as a slotted plate or screen may besubstituted for development electrode 178. Development electrode Wirespositioned substantially parallel to the direction of belt travel arepreferred when the electrode is stationary because developer particlejamming between the belt surface and electrode is substantially 8eliminated. As the developer composition becomes depleted of toner,additional toner material may be added through inlet 182.

The following examples further specifically define and describe thesystem of the present invention for developing electrostatographicimages in a stream of vibrating developer material moving in a generallycyclical path. Parts and percentages are by weight unless otherwiseindicated. The examples below are intended to illustrate the variouspreferred embodiments of carrying out the invention.

EXAMPLE I A xerographic drum coated with a 50 micron layer of vitreousselenium is corona charged to a voltage of about 500 volts and exposedto activating electromagnetic radiation to form a latent electrostaticimage on its surface. The selenium drum is then rotated while in contactwith a stream of vibrating developer material contained in a developerchamber such as that illustrated in FIG. 2 containing 600 micron coatedglass beads and 1 percent of a pigmented toner. The drum is rotated at alinear surface speed of approximately 4 inches per second in the samedirection as the developer stream flow in the development Zone. Anelectric vibrator securely attached to an external surface of thedeveloper housing is operated to provide an oscillatory vibrationfrequency of about 1,200 cycles per minute. After a single rotationthrough the developer stream, the image on the drum is transferred to asheet of paper and fixed by heat fusing. An excellent image is obtained.

EXAMPLE II A xerographic drum coated with a 50 micron layer of vitreousselenium is corona charged to a voltage of about 400 volts and exposedto a light and shadow image to form a latent electrostatic image. Theselenium drum is then rotated While in contact with a stream ofvibrating developer material contained in a developer chamber such asthat illustrated in FIG. 2 containing 250 micron coated steel beads and1 percent of a pigmented toner. The drum is rotated at linear surfacespeed of approximately 7 inches per second. A regular oscillatory motionwas imparted to the developer chamber by an electric motor havingunequal eccentric weights on the armature shaft. The motor was securelyattached to an external surface of the developer chamber and operated atabout 1,750 revolutions per minute to provide an oscillatory vibrationfrequency of about 1,750 cycles per minute. After a single rotationthrough the developer stream, the image on the drum is transferred to asheet of paper and fixed by heat fusing. A dense unsmeared image isobtained.

EXAMPLE III A xerographic flexible belt coated with 30 micron layer ofselenium is corona charged to a voltage of about 700 volts and exposedto a light and shadow pattern to form a latent electrostatic image onits surface. The portion of the xerographic belt bearing theelectrostatic latent image is brought into contact with a stream ofvibrating developer material contained within an electroded developerchamber such as that illustrated in FIG. 4 containing 500 micron coatedglass beads and 2 percent of a pigmented toner. The electrode comprisesWires, each l0 mils in diameter, spaced at A -inch intervals and spacedinch from the surface of the xerographic belt. The electrode is rigidlysecured to the ends of the developer chamber and are biased with a 350volt bias. The surface of the belt is caused to progress over thedeveloper material at a speed of approximately 10 inches per second inthe same direction as the developer flow. An electric vibrator such asthat illustrated in FIG. 3 is employed to provide an oscillatoryvibration frequency of about 2,500 cycles per minute. After a singlepass through the developer stream, the image on the belt is transferredto a sheet of paper and fixed by heat fusing. An image having good solidarea coverage is obtained.

Although specific components, proportions and procedures have beenstated in the above description of the preferred embodiments of thenovel developing system, other suitable materials, as listed above, maybe used with similar results. Further, other materials and proceduresmay be employed to synergize, enhance or otherwise modify the novelsystem. For example, the coefiicient of friction between the developermaterial and the surface of the xerographic drum and/or the surface ofthe developer chamber may be controlled by varying the composition ofthe developer and/or the surface of the xerographic drum or developerchamber to yield optimum results not inconsistent with good imagedevelopment.

Although corona charging is used in the examples, it should be notedthat any suitable method of forming an electrostatic latent image isdeemed within the scope of this invention. Additionally, any suitablesource of regular oscillatory vibrational energy such as the well knownroller type and turbine type vibrators may be employed to effectcyclical movement of the developer stream.

Other modifications and ramifications of the present invention willappear to those skilled in the art upon the reading of the disclosure.These are intended to be included within the scope of this invention.

What is claimed is:

1. A method of developing electrostatic latent images comprising thesteps of confining a dry bath of particulate developer materialcomprising toner particles in a chamber having an inner surfaceincluding an inner arcuate bottom surface, transmitting to saiddeveloper material in contact with said inner surface sufiicientnonlinear oscillatory motion defining a circuitous path to circulatesaid developer material as a flowing stream in an orbital path in asubstantially vertical plane around the central portion of said chamber,said oscillatory motion having an axis of oscillation perpendicular tosaid vertical plane and parallel to said inner arcuate bottom surfacewhereby said inner arcuate bottom surface of said chamber defines thecurved lowermost periphery of said orbital path, contacting the upperperiphery of said stream of developer material with a downwardly facingsurface bearing an electrostatic latent image whereby at least a portionof said toner particles deposit on said downwardly facing surface inimage configuration and removing said downwardly facing surface fromcontact with said upper periphery of said stream of developer material.

2. A method of developing electrostatic latent images according to claim1 including circulating said stream of developer material in acontinuously curved path by providing concave sides for said chamberjoining said arcuate bottom surface to form a smooth continuously curveddeveloper supporting surface parallel to the direction of said orbitalpath.

3. A method of developing electrostatic latent images according to claim1 including gradually changing the direction of said developer stream bycontacting a portion of said upper periphery of said stream of developermaterial with at least one curved lip, thereby eliminating the formationof stagnant areas of developer material adjacent said inner surface ofsaid chamber.

4. A method of developing electrostatic latent images according to claim1 including forming a zone of rapidly moving developer material along aportion of said upper periphery of said stream and a zone of slowlymoving developer material along another portion of said upper peripheryof said stream by confining said flowing stream of developer material ina U-shaped chamber.

5. A method of developing electrostatic latent images according to claim4 including contacting said downwardly facing surface with saiddeveloper material in said zone of rapidly moving developer material andthereafter contacting said downwardly facing surface with said developermaterial in said zone of slowly moving developer material.

6. A method of developing electrostatic latent images according to claim1 including introducing additional toner particles into said stream at apoint wherein said stream curves downwardly from said upper periphery ofsaid stream toward said arcuate bottom surface of said chamber, therebyreplenishing toner particles removed during development.

7. A method of developing electrostatic latent images according to claim1 including transporting an electrostatic latent image on the lowerexternal surface of a drum having a horizontal axis into contact withsaid upper periphery of said stream of developer material whilemaintaining said arcuate bottom surface of said chamber concentricallypositioned with respect to said lower surface of said drum.

8. A method of developing electrostatic latent images according to claim1 including maintaining a development electrode in said dry bath closelyadjacent and parallel to said imaging surface during development of saidelectrostatic latent image.

9. A method of developing electrostatic latent images comprising thesteps of confining a dry bath of particulate developer materialcomprising toner particles in a chamber having an inner surfaceincluding an inner arcuate bottom surface, trasmitting to said developermaterial in contact with said inner surface sufficient nonlinearoscillatory motion defining a circuitous path to circulate saiddeveloper material as a flowing stream in an orbital path in asubstantially vertical plane around the central portion of said chamber,said oscillatory motion having an axis of oscillation perpendicular tosaid vertical plane and parallel to said inner arcuate bottom surfacewhereby said inner arcuate bottom surface of said chamber defines thecurved lowermost portion of said orbital path, contacting the upperperiphery of said developer material with a moving downwardly facingsurface bearing an electrostatic latent image whereby at least a portionof said toner particles deposit on said downwardly facing surface inimage configuration and removing said moving downwardly facing surfacefrom contact with said upper periphery of said stream of developermaterial.

10. A method of developing electrostatic latent images comprising thesteps of confining a dry bath of particulate developer materialcomprising toner particles in a U- shaped chamber having an innersurface including an inner arcuate bottom surface, transmitting to saiddeveloper material in contact with said inner surface sufficieutnonlinear oscillatory motion defining a circuitous path to cir culatesaid developer materials as a flowing stream in an orbital path in asubstantially vertical plane around the central portion of said chamber,said oscillatory motion having an axis of oscillation perpendicular tosaid vertical plane, having an axis of oscillation parallel to saidinner arcuate bottom surface and having a frequency of from about 1,000cycles per minute to about 4,000 cycles per minute whereby said innerarcuate bottom surface of said chamber defines the curved lowermostperiphery of said orbital path, a zone of rapidly moving developermaterial along a portion of the upper periphery of said stream and azone of slowly moving developer material along another portion of saidupper periphery of said stream being formed by the confining of saidflowing stream of developer material in said U- shaped chamber,contacting a moving downwardly facing surface bearing an electrostaticlatent image with said developer material in said zone of rapidly movingdeveloper material, contacting said moving downwardly facing surfacewith said developer material in said zone of slowly moving developermaterial whereby at least a portion of said toner particles deposit onsaid moving downwardly facing surface in image configuration andremoving said moving downwardly facing surface from 11 contact with saidupper periphery of said stream of developer material.

11. A method of developing electrostatic latent images comprising thesteps of confining a dry bath of particulate developer materialcomprising toner particles and grossly larger carrier particles in achamber having an inner surface including an inner arcuate bottomsurface, transmitting to said developer material in contact with saidinner surface sufficient nonlinear oscillatory motion defining acircuitous path to circulate the developer material as a flowing streamin an orbital path in a substantially vertical plane around the centralportion of said chamber, said oscillatory motion having an axis ofoscillation perpendicular to said vertical plane, an axis of oscillationparallel to said inner arcuate bottom surface, a frequency ofoscillation from about 1,000 cycles per minute to about 4,000 cycles perminute, and an amplitude of oscillation from about .001 inch to about.25 inch, contacting the upper periphery of said stream of developermaterial with a moving downwardly facing surface bearing anelectrostatic latent image whereby at least a portion of said tonerparticles deposit on said moving downwardly facing surface in imageconfiguration and removing said moving downwardly facing surface fromcontact with said upper periphery of said stream of developer material.

12. A method of developing electrostatic latent images according toclaim 11 including imparting a nonlinear oscillatory motion to a shafthaving eccentric weights secured thereto, said oscillatory motion havingan axis of oscillation parrallel to the axis of said shaft, by rapidlyrotating said shaft and transmitting said oscillatory mo- 12 tion tosaid inner surface of said chamber whereby said nonlinear oscillatorymotion is imparted to said toner particles.

References Cited UNITED STATES PATENTS 2,759,450 8/1956 Vyverberg11717.5X 2,784,109 3/1957 Walkup 117-17.5 2,892,446 6/1959 Olden11717.5X 2,919,672 1/1960 Benn et a1 11717.5X 2,998,802 9/1961 Harris etal. 11717.5X 3,008,826 11/1961 Mott et a1 117-17.5X 3,011,473 12/1961Gundlach 11717.5X 3,013,890 12/1961 Bixby 118637X 3,059,614 10/1962Limberger 11717.5X 3,140,199 7/1964 York 118637 3,147,147 9/1964 Carlson118-637 3,254,625 6/1966 Armstrong 118-429X 3,257,223 6/1966 King11717.5 3,263,234 7/1966 Epstein et a1. 117-17.5X 3,283,334 11/1966Kutilc 118-637X 3,357,399 12/1967 Fisher 11717.5X

FOREIGN PATENTS 625,434 8/1961 Canada 11717.5

WILLIAM D. MARTIN, Primary Examiner E. I. CABIC, Assistant Examiner US.Cl. X.R. 1l8637

